Radiation shielded facilities, especially those involving high energy X radiation or neutron radiation, require particularly thick walls and barriers. As a consequence, these rooms need a shielded passageway or a long maze to prevent radiation from escaping the shielded space. Particle accelerators use electromagnetic fields to propel charged particles, such as electrons, protons, or ions, at high speeds along defined beams. One type of particle accelerator is a linear particle accelerator, also known as a linac, which increases the velocity of charged particles by subjecting the charged particles to a series of oscillating electric potentials along a linear beam line. Linacs are commonly used to generate x-rays for medical purposes. Due to radiation from particle accelerators, particle facilities must be designed and constructed to provide adequate shielding. Known particle facilities are generally constructed as a room housing the source of radiation, with concrete walls, ceilings, and floors that can reach thicknesses of up to 15 feet. In addition, a maze entry is usually used to provide a wing wall to capture scatter radiation. The entrance to a maze entry or direct entry particle facility includes at least one shielded door to further prevent radiation leakage to the outside of the room. The shielded door for a particle facility is generally constructed as a hinged door having a very thick core, for example 20 inches thick, to provide sufficient shielding. Known shielded doors are also extremely heavy, typically 10,000-20,000 lbs for medical radiation treatment rooms, and cannot be opened and closed quickly. The time that it takes to open and close a shielded door is especially important in particle facilities where an operator may need to enter and exit the room repeatedly to make adjustments. For example, in medical applications, several rounds of low energy radiation may be used for diagnostic purposes and patient positioning before treating the patient's tumor with the high energy radiation. After each round of low energy radiation, the operator must either progress down a very long maze corridor leading to the treatment room or alternatively wait for the shielded door to fully open before entering the treatment room to make adjustments to the patient, and then wait for the shielded door to fully close again before starting the next round of low energy radiation testing or high energy radiation treatment. This process can be very time consuming and tiring to the patient. In addition, in direct entry or mini maze entry particle facilities, two shielded doors may be required to ensure sufficient shielding at the entrance. Accordingly, the two shielded doors must be synchronized to open and close at the same time, or individually opened and closed, which further increases the time it takes to access the treatment room.
A need exists for an entrance assembly that is suitable for use in particle facilities, provides adequate shielding, and allows quick access in and out of the particle facility.